Macugen's black bubble.

When Macugen is injected into the vitreous, an air bubble is sometimes also
injected. The bubble appears black and appears to float around quite
quickly. (Not like moving around through a gel).

Why?

Don W.

 

When Macugen is injected into the vitreous, an air bubble is sometimes

I would almost assume that the bubble is a low index of refraction object
suspended in a higher index of refraction medium. Therefor (question) lens
optics dictates it leaves a shadow? Where do the incident light rays go??

Don W

PS. You owe me.

 

You are right that a gas bubble has *way* lower index than the
surrounding liquid and/or gel, so the roughly spherical "lens" it forms
would be strongly minus, so most incident rays (excepting a few axial
rays) are refracted at relatively large angles away from their optical
axes. Hence, a "shadow" on the retina.

w.stacy, o.d.

 

Thanks you. Talked to a person that had retinal surgery where a bubble was
used to constrain the retina. His bubble "appeared gray". Same logic I am
assuming. But here's my kicker question. The Macugen is injected into the
anterior of the vitreous. Very quickly, after the shot, the bubble freely
moves about. Like not suspended or stuck in a gel, but in a liquid. It
moves with head and eye position. How does it (appear to) get out of the
gel so quickly????? We're talking elder gels : )

Don W

 

Don W wrote:

Very quickly, after the shot, the bubble freely

When the (elder) vitreous contracts and detaches, it moves forward,
since it is more firmly attached at the front of the eye, leaving behind
a space that is filled with an aqueous fluid, which is where the bubble
is free to move.

w.stacy, o.d.

 

So the big question is how did it get out of the vitreous gel, where it is
presumably injected (front of the eye) into the posterior aqueous fluid????
I seem to have a problem in understanding that transistion. I don't see
(hmmm) the gel doing that, that quickly.

Don W.

 

I assume the injection was made in the pars plana area, which is really more the "side" of the eye than the "front" of the eye, and the posterior segment is quite reachable from there...

w.stacy, o.d.

Please excuse my delay. Assuming the radius of the cornea is R. The injection sites are at (approximately) 0.3R and at 0.7R (at about 7 o'clock) for the numbing shot and the Macugen off the cornea into the conjunctiva.

Don W.

 

They do go through the conjunctiva to get to the pars plana, which is
the normal route, and from there, through the sclera and into the
posterior vitreous. I don't think anyone touches the cornea for this
procedure.

w.stacy, o.d.

 

They do go through the conjunctiva to get to the pars plana, which is the normal route, and from there, through the sclera and into the posterior vitreous. I don't think anyone touches the cornea for this procedure.

My 0.3R and 0.7R are dimensions outside the outer rim of cornea into the conjunctiva. Sorry to use confusing nomenclature.

Don W